This invention relates to the anodization of aluminum foil, particularly for use in electrolytic capacitors. Even more particularly, it relates to an anodization electrolyte which reduces the electric charge requirements compared to conventional formation electrolytes.
The formation of dielectric barrier oxide films on aluminum foil for capacitors is known generally. These films are non-porous and quite thin (10.sup.-7 m). Generally, aqueous anodization electrolytes have been used for the anodization of aluminum, e.g., aqueous borate, phosphate, or citrate electrolytes. The use of non-aqueous electrolytes has been restricted usually to post-formation electrolytes, fill electrolytes for capacitors, or very specialized processes. Aqueous electrolytes are generally preferred since the solvent, water, is so much less expensive. Film quality also has been better when aqueous electrolytes have been used.
The industry always has been looking for ways to reduce electrical power consumption. A known way of doing this has been to anodize aluminum through a porous hydrated layer on its surface. However, hydrate formation cannot be used for low-volt anodization as fine pores become blocked. The search for means to reduce power consumption has intensified as energy costs have increased.